the effects of genetic variation

1. Within a species there is usually a great deal of
variation between individuals

2. ©JaneBurton
These snails are all
the same species
(Cepaea nemoralis)
but they vary
considerably
What variations
can you see ?
2

3. The snails’ shells vary in
•the presence or absence of bands
•the number of bands
• their colour
3

4. © Biophoto Associates
These tiger moths are
from the same family
What variations can
you see?
4

5. The uppermost moth is larger than the other two
The dark bands on the abdomen differ in number
and thickness
The patterns of the forewings are quite different
from each other
The number, shape and distribution of the black
spots on the hind wings differ
The amount of orange colour in the hind wings varies
5

6. You will already be familiar with many of the
variations between individuals of the human
species (Homo sapiens)
6

7. There are variations in skin colour, hair colour,
hair curliness, eye colour and sex
What variations can you see ? 7

8. Variations may be inherited or acquired
Inherited variations result from the activity of genes
They are genetically controlled
Genetically controlled variations cannot be altered
For example, hair colour, skin colour*, blood group,
finger prints and sex cannot be changed naturally
8

9. Acquired characteristics result from an individual’s
activities or nutrition or from environmental
conditions during a lifetime
Examples of acquired conditions in humans are*
language obesity
athletic skills mental skills
body building sun tan
Acquired characteristics cannot be inherited
9

10. The next side shows apples collected from different
positions on the same tree
The differences between the apples are acquired during
the growing season
The differences will not be inherited
10

11. North side, upper branches South side upper branches
North side, lower branches South side, lower branches
© Horticultural Research International
11

12. What environmental conditions in the different parts of
the tree might have caused the differences in size of the
apples ?
The upper branches will receive more sunlight than the
lower branches, but on the North side the sunlight would
have been less intense
The lower branches will receive less sunlight because of
the shade cast by the upper branches. This effect will be
more pronounced on the North side
12

13. A great many variations are influenced by both genetic
and environmental effects.
For example your height will depend on what genes
you inherit and the amount of food you get during your
growing period
You may inherit a good physique but unless you take
exercise you will not develop to your full potential
You may inherit the genes to make the pigment, melanin,
in your skin but you will need to expose your skin to
sunlight to acquire a tan
13

14. Discontinuous variation
Discontinuous variations are entirely genetically controlled
They cannot be altered by external conditions.
You are either male or female, there are no intermediates
Your ABO blood group is either A, B, AB or O
Genetic defects such as colour blindness, albinism,
achondroplastic dwarfism, sickle cell anaemia are all
Genetically controlled and expressed in a discontinuous way
(See ‘Heredity’ slide 19)
You either have these conditions or you do not. There are no
intermediate states
14

15. percentage
in population
of Britain
Discontinuous variation in blood group. The figures cannot
be made to fit a smooth curve because there are no intermediates
15

16. Continuous variation describes the situation in which there are
a great many intermediates between the extremes
For example, there is every shade of hair colour between black
and blond. People do not belong to one or other of a small number
of distinct categories
Variations such as these are under genetic control but there are
several pairs of genes involved
The genome AA BB CC DD might give black hair while the
genome aa bb cc dd might give blond hair.*
Genomes AaBbCcDd or AABbCCdd or aaBBccDd and all the
other possible combinations would give intermediate colours
Continuous variation
16

17. There are as
many categories
of hair colour as
there are children
17

18. Continuous variation also occurs when the characteristics
are controlled by the genes and the environment
Your height will depend on the genes you inherit and on
the amount of food you eat during your growing period
The next slide shows the range of heights of army recruits
See slide 13 for other examples
Continuous variation
18

19. thousands
of men
height in inches
There seem to be distinct categories of height but this is because
measurements are made to the nearest inch
19

20. If measurements could be made to the nearest millimetre
there would be a smooth transition in the heights
20

21. This is how continuous variation would appear in a graph
21

22. Question 1
Which of these statements are correct?
(a) Wild plants of the same species do not vary
(b) There is always variation between individuals
of the same species
(c) Individuals in the same species may show variations
(d) Daschunds and greyhounds are varieties of the same
species
22

23. Question 2
Variations in an individual’s weight…
(a) are entirely genetically controlled
(b) result exclusively from the amount of food
taken in
(c) are the result of food intake and genes
(d) are the result of chance
23

24. Question 3
Which of the following can be changed by
conditions other than genetic?
(a) Blood group
(b) Weight
(c) Physique
(d) Finger prints
24

25. Question 4
Which of the following are acquired characteristics ?
(a) Lung cancer
(b) Athleticism
(c) Curly hair
(d) Big feet
25

26. Question 5
Discontinuous variations are …
(a) inherited
(b) not inherited
(c) a combination of inherited
and acquired factors
(d) acquired during a lifetime
26

27. Question 6
Which of the following are examples of continuous
variation ?
(a) Height
(b) Weight
(c) Sex
(d) Intelligence
27

28. Answer
Correct
28

29. Answer
Incorrect
29